In recent years, lasers have been increasingly used for surgical operations within the eye. In one type of laser surgery, generally termed photocoagulation, a comparatively lower power laser beam from an argon or other visible spectrum laser is directed into the eye and onto a light absorbing target such as a leaking blood vessel or a retinal detachment. The heating of the target resulting from absorption of the energy of the laser beam results in coagulation of the target with beneficial results to the patient.
To assist a physician in accurately aiming the laser beam, it is common to produce a fluorescein angiogram of the eye prior to treatment. The fluorescein serves to highlight and locate the area surrounding the target. The angiogram is then used during the surgical operation as a guide to correct laser beam aiming. In the past, angiograms have been projected on a wall or otherwise displayed through a slide viewer such that the angiogram can be examined by the surgeon during the laser operation. Such prior techniques, however, require the surgeon to constantly shift his or her viewing between the angiogram and the image formed in the slit lamp. This shifting back and forth of the surgeon's view makes the process more time consuming, and also makes it more difficult to accurately aim the laser.